scholarly journals The Potential of Widespread Ready-Made UAVs in Quantifying Conifers and Delineating Their Crowns

2021 ◽  
Author(s):  
Jan Komárek ◽  
Petr Klápště ◽  
Karel Hrach ◽  
Tomáš Klouček
Keyword(s):  
Data Acquisition ◽  
Stand Structure ◽  
Low Cost ◽  
Tree Height ◽  
Ground Level ◽  
Absolute Error ◽  
Spectral Information ◽  
Individual Tree ◽  
Crown Delineation ◽  
The Individual

Abstract With the ever-improving Earth observation capabilities, variables such as tree health status, biomass storage, or stand structure are increasingly estimated through remote sensing. While many protocols of data acquisition and satellite data processing are in place, the still novel unmanned aerial vehicles (UAVs) face some challenges during data acquisition and processing. While tree height extraction seems to be a common practice, identifying individual trees and measuring their crowns is still quite tricky. We performed several flights with three different UAVs and four different popular sensors over two sites with coniferous forests of various ages at flight levels of 100–200 m above ground level (AGL) using custom settings preset by UAV solution suppliers. Considering the success rate of the individual tree identification, casual RGB cameras provided more consistent results at all flight levels (84 − 77% for Phantom 4), while the success of tree identification decreases with higher flight levels and smaller crowns in the case of multispectral cameras (77 − 54% for RedEdge-M). In general, RGB cameras yielded the best results at 150 m AGL while multispectral cameras at 100 m AGL. Regarding the accuracy of the measured crown diameters, most datasets tended to overestimate when using automatic crown delineation within the lidR package. Only RGB cameras yielded satisfactory results (Mean Absolute Error – MAE of 0.79–0.99 m and 0.88–1.16 m for Phantom 4 and Zenmuse X5S, respectively). Multispectral cameras overestimated more than RGB cameras, especially in the full-grown forest (MAE = 1.26–1.77 m); on the other hand, they offered, in addition to the structural, also spectral information. We conclude that widespread ready-made solutions mounted with low-cost RGB cameras yield very satisfactory results for describing the structural forest information at 150 m AGL. When (multi)spectral information is needed, we recommend reducing the flight level to 100 m AGL to acquire sufficient structural forest information.

scholarly journals Development and Performance Evaluation of a Very Low-Cost UAV-Lidar System for Forestry Applications

2020 ◽  
Vol 13 (1) ◽  
pp. 77
Author(s):  
Tianyu Hu ◽  
Xiliang Sun ◽  
Yanjun Su ◽  
Hongcan Guan ◽  
Qianhui Sun ◽  
...  
Keyword(s):  
Forest Inventory ◽  
Low Cost ◽  
Canopy Cover ◽  
Tree Height ◽  
Flying Height ◽  
Tree Level ◽  
Forest Site ◽  
Lidar System ◽  
Individual Tree ◽  
Gap Fraction

Accurate and repeated forest inventory data are critical to understand forest ecosystem processes and manage forest resources. In recent years, unmanned aerial vehicle (UAV)-borne light detection and ranging (lidar) systems have demonstrated effectiveness at deriving forest inventory attributes. However, their high cost has largely prevented them from being used in large-scale forest applications. Here, we developed a very low-cost UAV lidar system that integrates a recently emerged DJI Livox MID40 laser scanner (~$600 USD) and evaluated its capability in estimating both individual tree-level (i.e., tree height) and plot-level forest inventory attributes (i.e., canopy cover, gap fraction, and leaf area index (LAI)). Moreover, a comprehensive comparison was conducted between the developed DJI Livox system and four other UAV lidar systems equipped with high-end laser scanners (i.e., RIEGL VUX-1 UAV, RIEGL miniVUX-1 UAV, HESAI Pandar40, and Velodyne Puck LITE). Using these instruments, we surveyed a coniferous forest site and a broadleaved forest site, with tree densities ranging from 500 trees/ha to 3000 trees/ha, with 52 UAV flights at different flying height and speed combinations. The developed DJI Livox MID40 system effectively captured the upper canopy structure and terrain surface information at both forest sites. The estimated individual tree height was highly correlated with field measurements (coniferous site: R2 = 0.96, root mean squared error/RMSE = 0.59 m; broadleaved site: R2 = 0.70, RMSE = 1.63 m). The plot-level estimates of canopy cover, gap fraction, and LAI corresponded well with those derived from the high-end RIEGL VUX-1 UAV system but tended to have systematic biases in areas with medium to high canopy densities. Overall, the DJI Livox MID40 system performed comparably to the RIEGL miniVUX-1 UAV, HESAI Pandar40, and Velodyne Puck LITE systems in the coniferous site and to the Velodyne Puck LITE system in the broadleaved forest. Despite its apparent weaknesses of limited sensitivity to low-intensity returns and narrow field of view, we believe that the very low-cost system developed by this study can largely broaden the potential use of UAV lidar in forest inventory applications. This study also provides guidance for the selection of the appropriate UAV lidar system and flight specifications for forest research and management.

scholarly journals Adjudicating Perspectives on Forest Structure: How Do Airborne, Terrestrial, and Mobile Lidar-Derived Estimates Compare?

2021 ◽  
Vol 13 (12) ◽  
pp. 2297
Author(s):  
Jonathon J. Donager ◽  
Andrew J. Sánchez Meador ◽  
Ryan C. Blackburn
Keyword(s):  
Ponderosa Pine ◽  
Laser Scanning ◽  
Canopy Cover ◽  
Basal Area ◽  
Tree Height ◽  
Absolute Error ◽  
Forest Monitoring ◽  
Individual Tree ◽  
Structural Configurations ◽  
Individual Trees

Applications of lidar in ecosystem conservation and management continue to expand as technology has rapidly evolved. An accounting of relative accuracy and errors among lidar platforms within a range of forest types and structural configurations was needed. Within a ponderosa pine forest in northern Arizona, we compare vegetation attributes at the tree-, plot-, and stand-scales derived from three lidar platforms: fixed-wing airborne (ALS), fixed-location terrestrial (TLS), and hand-held mobile laser scanning (MLS). We present a methodology to segment individual trees from TLS and MLS datasets, incorporating eigen-value and density metrics to locate trees, then assigning point returns to trees using a graph-theory shortest-path approach. Overall, we found MLS consistently provided more accurate structural metrics at the tree- (e.g., mean absolute error for DBH in cm was 4.8, 5.0, and 9.1 for MLS, TLS and ALS, respectively) and plot-scale (e.g., R2 for field observed and lidar-derived basal area, m2 ha−1, was 0.986, 0.974, and 0.851 for MLS, TLS, and ALS, respectively) as compared to ALS and TLS. While TLS data produced estimates similar to MLS, attributes derived from TLS often underpredicted structural values due to occlusion. Additionally, ALS data provided accurate estimates of tree height for larger trees, yet consistently missed and underpredicted small trees (≤35 cm). MLS produced accurate estimates of canopy cover and landscape metrics up to 50 m from plot center. TLS tended to underpredict both canopy cover and patch metrics with constant bias due to occlusion. Taking full advantage of minimal occlusion effects, MLS data consistently provided the best individual tree and plot-based metrics, with ALS providing the best estimates for volume, biomass, and canopy cover. Overall, we found MLS data logistically simple, quickly acquirable, and accurate for small area inventories, assessments, and monitoring activities. We suggest further work exploring the active use of MLS for forest monitoring and inventory.

scholarly journals Stand structure links up canopy processes and forest management

2009 ◽  
Vol 51 (1) ◽  
pp. 40-48
Author(s):  
Toomas Frey
Keyword(s):  
Forest Management ◽  
Stand Structure ◽  
Net Primary Production ◽  
Stand Density ◽  
Tree Height ◽  
Belowground Biomass ◽  
Unit Mass ◽  
Total Biomass ◽  
Individual Tree ◽  
Mean Values

Stand structure links up canopy processes and forest management Above- and belowground biomass and net primary production (Pn) of a maturing Norway spruce (Picea abies (L.) Karst.) forest (80 years old) established on brown soil in central Estonia were 227, 50 and 19.3 Mg ha correspondingly. Stand structure is determined mostly by mean height and stand density, used widely in forestry, but both are difficult to measure with high precision in respect of canopy processes in individual trees. However, trunk form quotient (q2) and proportion of living crown in relation to tree height are useful parameters allowing describe stand structure tree by tree. Based on 7 model trees, leaf unit mass assimilation activity and total biomass respiration per unit mass were determined graphically as mean values for the whole tree growth during 80 years of age. There are still several possible approaches not used carefully enough to integrate experimental work at instrumented towers with actual forestry measurement. Dependence of physiological characteristics on individual tree parameters is the missing link between canopy processes and forest management.

Retrieving individual tree heights from a point cloud generated with optical imagery from an unmanned aerial vehicle (UAV)

2020 ◽  
Vol 50 (10) ◽  
pp. 1012-1024
Author(s):  
Meimei Wang ◽  
Jiayuan Lin
Keyword(s):  
Unmanned Aerial Vehicle ◽  
Point Cloud ◽  
Laser Scanning ◽  
Tree Height ◽  
Absolute Error ◽  
Coefficient Of Determination ◽  
Surface Model ◽  
Individual Tree ◽  
Aerial Vehicle ◽  
The Mean

Individual tree height (ITH) is one of the most important vertical structure parameters of a forest. Field measurement and laser scanning are very expensive for large forests. In this paper, we propose a cost-effective method to acquire ITHs in a forest using the optical overlapping images captured by an unmanned aerial vehicle (UAV). The data sets, including a point cloud, a digital surface model (DSM), and a digital orthorectified map (DOM), were produced from the UAV imagery. The canopy height model (CHM) was obtained by subtracting the digital elevation model (DEM) from the DSM removed of low vegetation. Object-based image analysis was used to extract individual tree crowns (ITCs) from the DOM, and ITHs were initially extracted by overlaying ITC outlines on the CHM. As the extracted ITHs were generally slightly shorter than the measured ITHs, a linear relationship was established between them. The final ITHs of the test site were retrieved by inputting extracted ITHs into the linear regression model. As a result, the coefficient of determination (R2), the root mean square error (RMSE), the mean absolute error (MAE), and the mean relative error (MRE) of the retrieved ITHs against the measured ITHs were 0.92, 1.08 m, 0.76 m, and 0.08, respectively.

Forty years of alternative management practices in second-growth, pole-size northern hardwoods. I. Tree quality deveSopment

1995 ◽  
Vol 25 (7) ◽  
pp. 1173-1179 ◽  
Author(s):  
Terry F. Strong ◽  
Gayne G. Erdmann ◽  
Jeffrey N. Niese
Keyword(s):  
Management Practices ◽  
Stand Structure ◽  
Control Treatment ◽  
Individual Tree ◽  
Northern Hardwood ◽  
Heavy Medium ◽  
Second Growth ◽  
Tree Quality ◽  
The Individual ◽  
Medium Selection

The effects of six cutting methods on tree quality were observed for 20 years in a northern hardwood stand in Wisconsin. Cutting treatments included an uncut control, three levels of individual tree selection (heavy, medium, and light), crop tree release, and diameter limit. Average annual diameter growth was least in the control treatment (0.13 in./year, 0.33 cm/year) and greatest in the heavy individual tree selection and diameter-limit cuts (0.18 in./year, 0.46 cm/year). Cull in trees in 1992 was significantly higher in the control and diameter-limit treatments. Changes in merchantable height (number of 16-ft (4.9-m) logs) over the period were not significantly different among treatments, but average merchantable heights were significantly greater in the individual tree selection treatments in 1992. Average tree grade increases were significantly better in the medium selection plots than in all other treatments except the crop tree release. Nearly a third of the sawlog-size trees in both the control and diameter-limit treatments were below sawlog grade, significantly more than in the other treatments. Only 2% of the trees in the heavy selection plots were below grade. Tree quality improved the most overall in the medium selection plots. Stand structure in this treatment also most closely matched that recommended by guides developed to sustain yield over long periods of cutting under uneven-aged management.

Development and evaluation of an automated tree detection–delineation algorithm for monitoring regenerating coniferous forests

2005 ◽  
Vol 35 (10) ◽  
pp. 2332-2345 ◽  
Author(s):  
D A Pouliot ◽  
D J King ◽  
D G Pitt
Keyword(s):  
Absolute Error ◽  
Tree Regeneration ◽  
Tree Size ◽  
Detection Accuracy ◽  
Individual Tree ◽  
Commission Errors ◽  
Tree Detection ◽  
Crown Diameter ◽  
Accuracy Index ◽  
The Individual

An algorithm is presented for automated detection–delineation of coniferous tree regeneration that combines strategies of several existing algorithms, including image processing to isolate conifer crowns, optimal image scale determination, initial crown detection, and crown boundary segmentation and refinement. The algorithm is evaluated using 6-cm pixel airborne imagery in operational regeneration conditions typically encountered in the boreal forest 5–10 years after harvest. Detection omission and commission errors as well as an accuracy index combining both error types were assessed on a tree by tree basis, on an aggregated basis for each study area, in relation to tree size and the amount of woody competition present. Delineation error was assessed in a similar manner using field-measured crown diameters as a reference. The individual tree detection accuracy index improved with increasing tree size and was >70% for trees larger than 30 cm crown diameter. Crown diameter absolute error measured from automated delineations was <23%. Large crown diameters tended to be slightly underestimated. The presence of overtopping woody competition had a negligible effect on detection accuracy and only reduced estimates of crown diameter slightly.

The accuracy of estimating individual tree variables with airborne laser scanning in a boreal nature reserve

2004 ◽  
Vol 34 (9) ◽  
pp. 1791-1801 ◽  
Author(s):  
M Maltamo ◽  
K Mustonen ◽  
J Hyyppä ◽  
J Pitkänen ◽  
X Yu
Keyword(s):  
Norway Spruce ◽  
Scots Pine ◽  
Laser Scanning ◽  
Stand Structure ◽  
Tree Height ◽  
Heterogeneous Structure ◽  
Mixed Stands ◽  
Individual Tree ◽  
Tree Layer ◽  
Pine Trees

This study examines the ability of high-density laser scanning to produce single-tree estimates in mixed stands of heterogeneous structure. Individual trees were detected from a constructed digital canopy height model by locating local maxima of the height values. The reference material comprised accurately measured field data for 10 mapped sample plots containing Norway spruce (Picea abies (L.) Karst.), Scots pine (Pinus sylvestris L.), and different birches. To verify the accuracy of height measurements of single trees in more detail, the height of 29 Scots pine trees and their annual shoots of the last few years was carefully measured with a tacheometer and a glass fibre rod. The considered variables were the proportion of detected trees and tree height. As more than 80% of the dominant trees were detected, the results indicated that laser scanning can accurately describe the trees of the dominant tree layer. Because of the dense understorey tree layer in most of the sample plots, about 40% of all trees were detected. On the plot level, the stand structure affected the accuracy of the results considerably. The scanning-based tree height was most accurate for Norway spruce and least accurate for birches. The height of the separately measured 29 Scots pine trees was obtained with an accuracy of ±50 cm or better.

scholarly journals Prediction of Diameter Using Height and Crown Attributes: A Case Study

2012 ◽  
Vol 27 (1) ◽  
pp. 30-35 ◽  
Author(s):  
Cosmin N. Filipescu ◽  
Arthur Groot ◽  
Dan A. MacIsaac ◽  
Mike G. Cruickshank ◽  
James D. Stewart
Keyword(s):  
Stand Structure ◽  
Mean Squared Error ◽  
Tree Height ◽  
Remotely Sensed ◽  
Stem Diameter ◽  
Remotely Sensed Data ◽  
Individual Tree ◽  
Crown Area ◽  
Effective Manner

Abstract Recent advances in remote sensing provide increasingly detailed forest information in a timely and cost-effective manner. Individual tree stem diameter, an important variable for operational forest inventory, cannot be determined directly from remotely sensed data; stem diameter must be estimated from ancillary measures of tree crown, tree height, and/or measures related to stand structure. In this study, we developed predictive models of diameter as a function of height and crown attributes using a nonlinear mixed-effects approach. Long-term silvicultural experiments provided data for several species: black spruce, Douglas-fir, and lodgepole pine. Addition of crown area and crown area of larger trees to diameter-height models significantly improved predictive performance, resulting in low root mean squared error values between 0.9 and 1.8 cm (10–11% of mean diameter). Our models indicated the need to include additional explanatory variables at wider levels of spacing and thinning. This case study highlights several practical implications for developing and refining individual tree diameter models based on variables that can be remotely sensed.

Intra- and Inter-Tree Variability of Moisture Content in Standing Sessile Oak (Quercus petraea Liebl.)

Holzforschung ◽  
2002 ◽  
Vol 56 (2) ◽  
pp. 117-124 ◽  
Author(s):  
T. Constant ◽  
G. Nepveu ◽  
F. Huber
Keyword(s):  
Moisture Content ◽  
Stand Structure ◽  
Tree Height ◽  
Quercus Petraea ◽  
Site Quality ◽  
Average Moisture Content ◽  
Sessile Oak ◽  
Tree Effect ◽  
The Individual

Summary Knowledge about the moisture content of trees in the forest or wood yard is scarce. The variation of moisture content within and between 20 boles of sessile oak was investigated using 1543 measurements performed at three heights in each tree and along 4 radii. Five radial positions were defined: sapwood, outer, intermediate and inner heartwood, and the core piece including the pith. Results show that the average moisture content is highly dependent on the individual. The average moisture content was around 80%(oven-dried basis), but it ranges from 65% to 100%depending on the tree. This “tree” effect is discussed and examined using some general characteristics of the trees (region, stand structure, site quality, dendrometric and densitometric traits). Apart from age counted from pith, and the ratio of tree height vs. diameter, no strong correlation appears. Moderate variations in moisture content with radial position and height are also brought to the fore. The specific role of sapwood, which exhibits a more variable moisture content is discussed.

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